Gas turbine engines such as utilized in aircraft are characterized by a relatively highly complex mechanical design of a variety of components. Assembly, aftermarket support, repair and overhaul of such complicated machinery may be time consuming and relatively expensive. To facilitate field support of such engines, more modern designs are modular in concept. This means the engine is designed into a plurality of subassemblies or modules, few in number, which may be individually removed or assembled to the remainder of the engine modules. Thus, such a modularly designed engine allows the removal and replacement of a single module in the field so that the engine may be returned to service as rapidly as possible. The removed module may then be fully disassembled, repaired and/or overhauled at a remote site with minimal overall engine or aircraft down time.
An important consideration in such modularly designed engines is that the components designed to be carried as a single modular subassembly be interrelated to one another regarding frequency of required overhaul and/or susceptibility of failure or damage during the life of the engine. From this it will be apparent that there are economic disadvantages in designing into a single module a group of components having significantly greater life expectancy or overhaul frequency, than another group of components therewithin, since the components with greater life expectancy would be required to be disassembled and replaced from the operating engine at the same frequency as the components with lower life expectancy.
One complexity in designing a modular gas turbine engine relates to the central through shaft assembly which may be typically supported to the engine stationary structure at locations adjacent the forward and aft ends of the engine. The design of a modular subassembly disposed wholly intermediate these shaft supports often leads to difficulties in accessibility and tooling for assembly and disassembly of the intermediate module without disturbing the central shaft assembly.